(notice that even though my locale is here in London, because of the summer time an hour is added)

Well, I thought I'd do a quick benchmark to compare the two approaches because I suspected that rfc1123_date() was faster because you don't have to create a DateTime() object. Here's what the two methods looked like to benchmark it:

But a benchmark on something like this is a bit non-sense. Why? Because even if there's a 7 times difference, you'll only ever need one of these iterations per page. Not 10,000. The first function foo1() takes 0.00013 seconds.

Conclusion, worry more about getting the right output rather than speed at this kind of level.